In several communications systems the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
The above-referenced standards describe data processing and manipulation techniques that are well suited to the compression and delivery of video, audio and other information using fixed or variable length digital communications systems. In particular, the above-referenced standards, and other "MPEG-like" standards and techniques, compress, illustratively, video information using intra-frame coding techniques (such as run-length coding, Huffman coding and the like) and inter-frame coding techniques (such as forward and backward predictive coding, motion compensation and the like). Specifically, in the case of video processing systems, MPEG and MPEG-like video processing systems are characterized by prediction-based compression encoding of video frames with or without intra- and/or inter-frame motion compensation encoding.
In a typical MPEG encoder, a received video stream comprising a plurality of video frames is encoded according to a predefined group of pictures (GOP) structure. That is, the received video stream is encoded to produce a GOP comprising, e.g., an intra-coded frame (I-frame), followed by one or more forward predicted coded frames (P-frames) and bi-directional (i.e., forward and backward) predicted frames (B-frames).
Unfortunately, since motion compensation techniques are not perfect, predicted frames or pictures may suffer from undesirable visual artifacts such as error propagation, reduced editing granularity and the like. Moreover, GOP structures including such predicted frames also suffer from such artifacts. Since the fidelity of individual frames within a GOP structure tend to degrade after an initial high quality I-frame, the display of a sequence of GOPs produces a cyclical visual artifact known as "breathing," where the cyclical nature of the artifact is related to the length of the GOPs displayed.
Therefore, it is seen to be desirable to provide a method and concomitant apparatus that reduce the above-described "breathing" artifact.